1. Field of the Invention
The present invention relates to the production of maleic acid, its isomer fumaric acid, the anhydride of either maleic or fumaric acid (maleic anhydride) and, more particularly, the oxidation of levulinic acid to yield maleic acid, fumaric acid, or maleic anhydride.
2. Description of the Related Art
Concern over diminishing fossil reserves has increased interest in the production of industrial commodities (transportation fuels, commodity chemicals, etc.) from biomass resources. In particular, lignocellulosics (e.g., woody biomass) are viewed as an ideal alternative source of industrial carbon (i.e., alternative to petroleum) since they are abundant, easily cultivated, often grow on marginal land, and require minimal resource inputs compared to conventional food crops.
Despite the interest in establishing lignocellulosic biorefineries on a large scale, no technologies have to date proven cost effective. The source of the lack of economic viability despite a myriad of potential options for biomass processing is complex; however, it can be generally summarized as a tension between the ease of converting biomass to a potentially useful industrial commodity and the revenue that can be generated from said product. In general, transportation fuels are a difficult market to enter as lignocellulosic fuels must compete with relatively low cost petroleum and a well-optimized refinery structure built around the large scale production of transportation fuels. Despite large markets in the transportation sector, biofuels—particularly lignocellulosic biofuels—have been unable to compete with conventional fuels. Further, they are unlikely to be competitive with petroleum-based fuels for the foreseeable future. Even inexpensive lignocellulosic commodities, such as pyrolysis oils, require extensive upgrading before their properties match those of the hydrocarbon fuels required in the current infrastructure. As such, lignocellulosic fuels will likely remain prohibitively expensive in the near term. In contrast, chemical products are relatively difficult to derive from petroleum and generally offer higher profit margins. Further, chemical targets are often more straightforward to produce from biomass than via competing peteroleum based strategies. This suggests that lignocellulosic chemical products could be economically viable in the near term, allowing a portion of the peterochemicals industry to shift toward using renewable feedstocks.
Levulinic acid, as seen in FIG. 1, is one such example of an attractive chemical product that is relatively easy to source from lignocellulose. The entire carbohydrate content of lignocellulose (i.e., hemicellulose, cellulose, and sugars derived therefrom) can be converted into levulinic acid using well established technologies. For example, the BioFine Process has been optimized to produce Levulinic acid from six-carbon sugars such as the glucose subunits forming cellulose in yields as high as 75% of the theoretical maximum. If five-carbon sugars are present in biomass, they are converted to furfural by acid hydrolysis and can be recovered as co-products of LA production. Furfural is presently produced at commodity scales by acid hydrolysis of xylan rich corn waste (e.g., cobs). Once formed, furfural can be converted to levulinic acid in high yields by sequential hydrogenation (to form furfuryl alcohol) and hydrolysis (to form levulinic acid). Given that C5 and C6 sugars generally comprise up to 80 wt % of lignocellulose, LA appears to be an attractive chemical intermediate that is relatively easy to produce from sugars and can utilize a large fraction of the available feedstock.
Presently, LA is a relatively expensive chemical intermediate, and no existing industry relies on this molecule as a precursor; as such, despite its straightforward production, there are presently no large scale off-takers for LA, and development of the industry has largely stalled despite its promise. This has motivated research to identify strategies by which LA can be easily converted into a target product that does have a robust market. Much of the effort has pursued efficient production of transportation fuels from LA; however, no matter how efficient the upgrading, LA-based fuels are not yet competitive with petroleum derived alternatives.